University learnersMeasure and inferExample · 1 question · 2 min

Circuit Parameter Identification

Inspect a measured resistor circuit, infer one resistance from two states, carry uncertainty through the calculation, and test it against a third state.

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Voltage and current measurements

State	Voltage	Current
1	6.02 ±0.06 V	0.502 ±0.006 A
2	11.96 ±0.12 V	0.997 ±0.010 A
Check	9.00 ±0.09 V	0.748 ±0.011 A

A resistor at 20 °C is measured three times. State 1: 6.02 V and 0.502 A. State 2: 11.96 V and 0.997 A. Check state: 9.00 V and 0.748 A. Each value carries about 1% uncertainty.

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A resistor at 20 °C is measured at 6.02 V and 0.502 A, then at 11.96 V and 0.997 A. Which resistance fits both states and predicts the check state at 9.00 V?

About 6.0 Ω: it predicts 1.50 A at 9.00 V.About 12.0 Ω: it predicts 0.750 A at 9.00 V.

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Calculate V divided by I for each measurement separately, then use R = 12.0 Ω to predict the third current.

About this activity

What you practise: Write the check as a model report: R = 12.0 ±0.2 Ω at 20 °C ±1 °C; predicted I at 9.00 ±0.09 V is 0.750 ±0.011 A, compared with 0.748 ±0.011 A measured.

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A resistor at 20 °C is measured at 6.02 V and 0.502 A, then at 11.96 V and 0.997 A. Which resistance fits both states and predicts the check state at 9.00 V? A resistor at 20 °C is measured three times. State 1: 6.02 V and 0.502 A. State 2: 11.96 V and 0.997 A. Check state: 9.00 V and 0.748 A. Each value carries about 1% uncertainty. Use R = V/I for each state: 6.02 V ÷ 0.502 A ≈ 12.0 Ω and 11.96 V ÷ 0.997 A ≈ 12.0 Ω. With 12.0 Ω, 9.00 V gives I = 9.00 ÷ 12.0 = 0.750 A, within the uncertainty of the measured 0.748 A. 6.0 Ω would predict 1.50 A, twice the measured current.